Gold-containing catalysts for the removal of hydrogen from oxygen-rich streams.

Abstract

A process for removing hydrogen from an oxygen gas stream includes electrolyzing water in an electrolytic cell to produce a hydrogen-rich stream and an oxygen-rich stream. The oxygen-rich stream includes hydrogen. The process also includes supplying the oxygen-rich stream to a reactor having a gold-containing catalyst and contacting the oxygen-rich stream with the gold-containing catalyst in the reactor. The gold-containing catalyst includes gold and a second metal on an oxide support, and the oxygen-rich stream in the reactor has an oxygen partial pressure greater than 1 bar.

Description

[Technical Field]

[0001] This disclosure relates to the removal of hydrogen from oxygen-rich streams. More specifically, this disclosure relates to gold-containing catalyst compositions and methods of making gold-containing catalyst compositions for use in the removal of hydrogen in oxygen-rich streams. [Background technology]

[0002] As the transition from fossil energy carriers to low-carbon energy solutions continues to progress, there is a demand for alternative, non-fossil energy sources. One such low-carbon energy carrier is hydrogen. Hydrogen can be produced by thermochemical conversion (e.g., from biogas or natural gas) or by electrolysis, which splits water into hydrogen and oxygen. Hydrogen produced via electrolysis using green power as an energy source is of particular interest because this hydrogen (also known as green hydrogen) has the lowest greenhouse gas emissions compared to other technologies used to produce hydrogen. The electrolysis of water to form hydrogen and oxygen takes place in an electrolyzer with an anode and cathode separated by an electrolyte. At the anode, water reacts to produce oxygen (O2) and hydrogen ions (H + ) is formed. H + The ions migrate across the electrolyte to the cathode side of the electrolyzer to form hydrogen gas (H2), which outputs an H2 gas stream that is further treated to remove contaminating amounts of oxygen and water before use.

[0003] In addition to the H2 gas stream, the electrolyzer also outputs an O2-rich stream. The O2-rich stream can also be used for various purposes. To enable safe storage, safe transportation, and optimal use, this O2-rich stream must be further processed to remove contaminating amounts of water and H2 gas. Furthermore, H2 is considered to act as a greenhouse gas. Therefore, removal of H2 from certain gas streams, such as O2-rich streams, may be required by government agencies prior to use and / or release into the environment. One technique for removing H2 gas from an O2-rich stream is catalytic oxidation, in which hydrogen reacts with excess oxygen in a catalytic converter to produce water. This water is then removed downstream in a separate unit. For example, palladium (Pd) and platinum (Pt)-based catalysts are used in the deoxygenation of H2 gas streams. In Hanson et al., the reaction between H2 and O2 over a supported platinum catalyst was evaluated. (Hanson et al., The Reaction between H2 and O2 over Supported Platinum Catalysts, Journal of Catalysis, 53, pages 56-67.) However, these catalysts are unsuitable for the removal of H2 from oxygen-rich streams. In oxygen-rich environments, at elevated pressures and temperatures below 100 degrees Celsius (°C), these catalysts have been found to exhibit much lower activity than would be expected when compared to the same reaction in an oxygen-lean environment. Therefore, it would be advantageous to develop catalysts with desirable activity and stability for use in removing H2 from O2-rich streams at low temperatures. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Hanson et.al, The Reaction between H2 and O2 over Supported Platinum Catalysts, Journal of Catalysis, 53, pages 56-67. Summary of the Invention

[0005] In one embodiment, a process for removing hydrogen from an oxygen gas stream includes electrolyzing water in an electrolytic cell to produce a hydrogen-rich stream and an oxygen-rich stream. The oxygen-rich stream includes hydrogen. The process also includes supplying the oxygen-rich stream to a reactor having a gold-containing catalyst and contacting the oxygen-rich stream with the gold-containing catalyst in the reactor. The gold-containing catalyst includes gold and a second metal on an oxide support, and the oxygen-rich stream in the reactor has an oxygen partial pressure greater than 1 bar.

[0006] Additional features and advantages of exemplary implementations of the present disclosure will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by the practice of such exemplary implementations. The features and advantages of such implementations may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features will become more fully apparent from the following description and the appended claims, or may be learned by the practice of the exemplary implementations described hereinafter. [Brief explanation of the drawings]

[0007] Advantages of the present disclosure may become apparent upon reading the following detailed description and upon reference to the drawings. [Figure 1] FIG. 1 is a block diagram of a system having an electrolyzer and a hydrogen removal reactor comprising a catalyst for removing hydrogen (H) from an oxygen (O)-rich stream produced in the electrolyzer, according to one embodiment of the disclosure. [Figure 2] FIG. 2 is a flow diagram of a method for making a bimetallic catalyst for use in removing H from an O-rich stream produced in the system of FIG. 1 according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] One or more specific embodiments of the present disclosure are described below. The described embodiments are examples of the technology of the present disclosure. Moreover, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described herein. It should be understood that, as in any engineering or design project, the development of any such actual implementation will involve numerous implementation-specific decisions to achieve the developer's particular goals, including compliance with system- and business-related constraints, which may vary from implementation to implementation. It should also be understood that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill in the art having the benefit of this disclosure.

[0009] When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. In addition, it should be understood that references to "one embodiment" or "embodiments" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0010] As used herein, the terms "approximately," "about," and "substantially" refer to an amount close to the stated amount that still performs the desired function or achieves the desired result. For example, the terms "approximately," "about," and "substantially" can refer to an amount that is within less than 10%, less than 5%, less than 1%, less than 0.1%, and less than 0.01% of the stated amount.

[0011] The energy transition has created opportunities for alternative fuels and energy solutions that significantly reduce or eliminate carbon dioxide (CO2) emissions compared to traditional fossil fuels. An attractive alternative energy solution is hydrogen, in part due to its high energy density and zero CO2 emissions. Various types of hydrogen (e.g., gray, blue, green, etc.) exist depending on their source. For example, hydrogen produced via the thermochemical conversion of natural gas is known as gray hydrogen. Blue hydrogen is also produced through the thermochemical conversion of natural gas. However, the difference between gray and blue hydrogen is that in blue hydrogen, CO2 is captured and stored underground. Green hydrogen is produced from renewable sources and has the lowest CO2 emissions compared to gray and blue hydrogen.

[0012] Green hydrogen can be produced through the decomposition of water (H2O) via electrolysis. In electrolysis, water is electronically split into hydrogen (H2) gas and oxygen (O2) gas to produce an H2-rich output steam and an O2-rich output stream. The H2-rich output stream has contaminating amounts of O2 and water. Similarly, the O2-rich output stream has contaminating amounts of H2 and water. These contaminants are removed from the output stream before use. Several precious metal-based catalysts exist for removing O2 and H2 from various streams. For example, palladium (Pd) and / or platinum (Pt)-based catalysts are used to catalyze reactions for the removal of O2 and H2. Generally, these catalysts are used for the removal of O2 from H2-rich output streams, the selective removal of H2 from hydrocarbon or carbon monoxide (CO) streams, and the removal of H2 accumulation in batteries. For these applications, typical reaction conditions in these catalytic processes can be inlet temperatures below about 100 degrees Celsius (°C). Furthermore, these applications are typically run at relatively low oxygen partial pressures (e.g., O2 partial pressures less than about 0.2 bar, similar to the partial pressure of oxygen in air). However, the O2 partial pressure in the O2-rich output stream produced from water electrolysis generally ranges from about 1 bar to about 5 bar or more. Noble metal-based catalysts, such as Pd, Pt, or Pd / Pt-based catalysts, typically applied in catalytic reactions between hydrogen and oxygen have been found to have undesirable performance when temperatures are below 160°C, particularly below 100°C, and when O2 partial pressures exceed 1 bar (e.g., 5 bar). That is, these noble metal-based catalysts have poor activity and stability and are subject to oxidation in O2-rich environments.

[0013] For example, the effect of oxygen partial pressure on the catalytic performance of a Pd catalyst having 0.5 wt.% Pd is illustrated in Table 1. This catalyst represents a prior art noble metal-based catalyst, considered herein as a comparative sample, and its preparation is provided in Example 3 below. In Example 1, the Pd catalyst was subjected to an O2 partial pressure of 5 bar, an H2 concentration of 1000 parts per million volume (ppmv) (i.e., 5 millibars (mbar)), and a 10,000 hr -1The Pd catalyst was contacted with a gas stream simulating the electrolyzer O2 off-gas stream, having a gas hourly space velocity of 1000 ppmv and a temperature of 115°C. For comparison, in Example 2, the Pd catalyst was contacted with a gas stream having the same H2 concentration of 1000 ppmv, but in which most of the O2 had been replaced with nitrogen (N2) gas to reduce the O2 partial pressure from 5 bar to 0.25 bar. The concentration of H2 was measured in the outlet gas and is shown in Table 1 below.

[0014] [Table 1]

[0015] As shown in Table 1, the performance of the Pd catalyst is undesirable at high O partial pressures (e.g., 5 bar) based on a 40% H conversion rate compared to low O partial pressures (e.g., 0.25 bar). Without being bound by theory, the degradation of catalytic performance of the Pd catalyst in the presence of O-rich gas is believed to be due, in part, to the oxidizing environment created by O gas at high O partial pressures (e.g., 5 bar). This high oxygen partial pressure oxidizes the reactive sites of the Pd nanoparticles present in the catalyst, thereby preventing reaction with hydrogen. To achieve the activity required for high conversion rates at the required gas hourly space velocity, the oxidized Pd catalyst must be reactivated by reduction in an oxygen-free environment at regular intervals, which can range from several hours to several months, depending on the standard conditions and the manner in which the reactor is operated. Such operation is undesirable.

[0016] Another technique for improving catalyst performance to achieve high conversion rates for a given gas hourly space velocity is to increase the reaction temperature. However, in O2-rich environments and O2 partial pressures above 1 bar, increasing the reaction temperature is suboptimal and complicated, as it can raise safety concerns and affect the equipment metallurgy due to reactions with equipment surfaces in contact with the O2-rich gas.

[0017] Additionally, the presence of water vapor in the electrolyzer O2-rich off-gas adds further complications and also affects catalyst performance. For example, the electrolyzer O2-rich off-gas may have a dew point close to the temperature of the electrolyzer used for water electrolysis, which is approximately 57°C, corresponding to approximately 0.17 bar. Furthermore, unlike the electrolyzer H2-rich off-gas, which promotes self-activation of the precious metal catalyst through self-reduction, the electrolyzer O2-rich off-gas promotes oxidation, as discussed above. Thus, when a precious metal catalyst is used to treat an O2-rich stream, it is oxidized, and its catalytic performance and stability are reduced compared to reduced precious metal catalysts. However, as discussed in more detail below, it has surprisingly been found that incorporating gold (Au) into the catalyst improves the catalytic performance and stability of precious metal catalysts when used to remove hydrogen from an O2-rich stream.

[0018] With the foregoing in mind, FIG. 1 is a block diagram of a system 10 that may be used in a process for producing an oxygen-rich stream having a contaminant level of H and removing H from the oxygen-rich stream. As discussed in detail below, the system 10 uses a catalyst of the present disclosure to remove H from the oxygen-rich stream and includes an electrolyzer 14 and a hydrogen removal reactor 16. In the illustrated embodiment, the electrolyzer 14 receives a water (H2O) stream 20 through an inlet 24 and, via electrochemistry, splits the water in the H2O stream 20 into a hydrogen (H2)-rich stream 28 and an oxygen (O2)-rich stream 30. The electrolyzer 14 includes a first outlet 32 ​​for outputting the H2-rich stream 28 and a second outlet 36 for outputting the O2-rich stream 30. The splitting of water via electrolysis is a process well known in the art and will not be described in detail. As discussed above, an O2-rich stream produced from the electrolysis of water, such as the O2-rich stream 30, has a contaminant amount of H2. Thus, prior to use, contaminating amounts of H in the O2-rich stream 30 are removed. Thus, as shown in the illustrated embodiment, the O2-rich stream 30 is fed to the reactor 16 through a reactor inlet 38. The reactor 16 includes one or more catalyst beds 40 having a gold-containing hydrogen removal catalyst 42. In the reactor 16, the O2-rich stream 30 contacts the catalyst 42 to remove contaminating amounts of H, thereby producing a treated O2-rich stream 46 that is essentially free of H2 (e.g., containing less than about 50 ppmv H2, preferably less than 10 ppmv). Thus, the treated O2-rich stream 46 may have approximately 95-100% less hydrogen compared to the O2-rich stream 30. The treated O2-rich stream 46 is discharged from the reactor 16 through a reactor outlet 50 and may be further processed in subsequent downstream processes. Depending on the use of the treated O2-rich stream 46, the subsequent process may remove water vapor from the stream 46. Between the second outlet 36 and the reactor inlet 38, elements such as heating elements, compressor elements, drying elements, contaminant removal elements, and combinations thereof may be added.

[0019] An essential part of the system disclosed herein is the electrolyzer 14. Those skilled in the art will clearly recognize that there are various technologies and configurations capable of electrolyzing water. Currently, there are three main water electrolysis technologies used on a commercial scale, including 1) alkaline water electrolysis (AEL), 2) polymer electrolyte membrane (PEMEL), and 3) solid oxide electrolyte (SOEL). In all these technologies, gas crossover (e.g., H2 migration to the O2 side and vice versa) is observed through the membrane separating the cathode from the anode compartment. As a result, hydrogen gas formed on the cathode side leaks into oxygen gas produced at the anode, and therefore, it is necessary to remove contaminant gases (e.g., H2 or O2) from the respective gases downstream of the electrolyzer 14.

[0020] In the reactor 16, the gold-containing hydrogen removal catalyst 42 removes H from the O-rich stream 30. Surprisingly, it has been discovered that at O ​​partial pressures in the range above about 1 bar, the gold-containing hydrogen removal catalyst 42 has improved activity and performance compared to non-gold-containing precious metal hydrogen removal catalysts. The reactor 16 may include one or more of a fixed-bed reactor, a fluidized-bed reactor, or both. In one embodiment, the catalyst bed 42 is a stacked bed. In a preferred embodiment, the catalyst bed 42 has a packed catalyst bed configuration in which the catalyst is fixed inside the reactor 16. The packed catalyst bed configuration may be uncooled (e.g., an adiabatic reactor), cooled (e.g., to promote isothermal behavior), or both. Because the reaction between H and O is exothermic, an uncooled catalyst bed configuration in which heat is not removed from the catalyst bed results in an increase in the temperature of the O-rich stream 30 in the reactor 16 as the reaction propagates through the length of the catalyst bed 40. Eventually, the O2-rich stream 30 in the reactor 16 reaches a final adiabatic temperature rise. However, in a cooled catalyst bed configuration, heat is continuously removed throughout the length of the catalyst bed 40. Therefore, the temperature of the O2-rich stream 30 may remain at or near the temperature of the reactor inlet 38 and not reach an adiabatic temperature rise. In embodiments in which the catalyst bed 40 is a cooled catalyst bed configuration, the bed 40 may be a multi-tubular packed bed having a catalyst 42 packed in tubes surrounded by a heat exchange medium. The heat exchange medium may be water, steam, oil, molten salt, or any other suitable heat exchange medium, and combinations thereof. The catalyst bed 42 of the present disclosure may be arranged in a variety of ways. For example, the catalyst bed 42 may have a single catalyst (e.g., catalyst 42) that fills a majority of the internal volume of the reactor 16. The catalyst 42 may be supported by a grid that retains the catalyst 42 within the reactor 16 while allowing the treated O2-rich stream 46 to flow through the catalyst bed 40 and exit the reactor 16. In a preferred embodiment, a support bed between the grid and catalyst bed 40 is made of an inert material having grains larger in size than the catalyst 42 (e.g., spherical support bed grains generally having diameters of about 1 millimeter (mm) to 20 mm, depending on catalyst particle size). Such a support bed helps to avoid clogging of the grid with relatively small catalyst grains (e.g., grains having diameters of about 0.5 mm to 4 mm).In another embodiment, the catalyst bed 40 is covered by a guard bed designed to capture contaminants present in the O2-rich stream 30 that could potentially harm (e.g., poison) the catalyst 42. As an example, the oxygen stream coming from an alkaline electrolyzer may carry small amounts of aqueous aerosols containing high levels of potassium hydroxide (KOH). A guard bed with high pore volume and / or acidic properties can help capture such aerosols while neutralizing and absorbing the alkaline KOH. Typical examples of such guard beds are activated alumina, silica, and / or silica gel. Such guard beds also help buffer the relative humidity of the O2-rich stream 30. When the relative humidity becomes high and reaches concentrations approaching 100%, such guard beds can temporarily absorb water vapor during these extreme conditions.

[0021] In an alternative embodiment, two or more different catalyst materials with different compositions are stacked on top of each other and loaded into the bed. For example, catalyst bed 40 may have a first bed with a first catalyst (e.g., catalyst 42) filling its volume, and a second bed with a second catalyst (e.g., catalyst 42) that is different from the first catalyst, filling its volume. Such a configuration may facilitate optimization of catalyst performance. The first catalyst may be located in the upstream portion of catalyst bed 40, where the hydrogen concentration is still relatively high compared to the downstream portion of catalyst bed 40. The first catalyst is designed to have higher activity at low temperatures compared to the second catalyst. The second catalyst is located in the downstream section of catalyst bed 40 and is more robust to higher temperatures and has better performance at very low hydrogen concentrations compared to the first catalyst.

[0022] The catalysts 42 disclosed herein are preferably formed into grains of sufficient size and intergranular porosity to produce a catalyst bed (e.g., catalyst bed 40) with a low pressure drop. The preferred shape of these catalysts is uniform / regularly shaped grains. The catalyst grains may be pellets and / or extrudates. By way of non-limiting example, the pellets and / or extrudates may be spherical, multi-lobed, rod-shaped, cylindrical, hollow, porous, and combinations thereof. Irregularly shaped catalyst grains, although less preferred, may also be used in catalyst bed 40. For fixed-bed applications, the diameter of the catalyst grains may range from about 0.5 mm to about 4 mm. For extrudates and pellets, the length may be significantly greater than the diameter, and the length may range from about 1 mm to about 10 mm. For fluidized-bed applications, the catalyst grains may have a particle size distribution such that at least 60% of the catalyst particles have a particle diameter below about 200 microns and no more than about 40% of the catalyst particles have a diameter less than about 40 microns.

[0023] As an alternative to a packed catalyst bed, the catalyst 42 may be formed into a catalytically active structure, whereby the structure is optimized to minimize pressure drop and maximize accessibility to the catalyst 42. By way of non-limiting example, the structure of the catalyst 42 may be a honeycomb, monolith, corrugated foil, or foam. Such structures have numerous small repeating elements, such as walls, foils, and struts. Both these elements and the cavities between them have dimensions of approximately 0.2 to 4 mm. The catalytically active structures of the catalyst 42 have dimensions much larger than the repeating elements they contain, which may range from approximately 5 mm to approximately 600 mm. The catalytically active material of the catalyst 42, which is a combination of gold (Au), a second metal, and an oxide support, may be part of the structure or present as a coating on the structure. In the latter case, the coating may have a thickness of approximately 0.05 mm to approximately 1 mm.

[0024] As discussed above, catalyst 42 contains Au mixed with another metal (i.e., a second metal) on an oxide support. The second metal can be selected from metals in Group VIIIB and / or Group IB of the Periodic Table of Elements, with all metals having hydrogen activation functionality being preferred. By way of non-limiting example, the second metal can be selected from nickel (Ni), cobalt (Co), copper (Cu), iridium (Ir), platinum (Pt), rhenium (Re), palladium (Pd), rhodium (Rh), and combinations thereof. Most preferred are noble metals, such as Pd, Pt, and Rh, which are believed to have a greater tendency to tolerate high oxygen partial pressures. In addition to the second metal, the catalyst may also contain a third or more additional metals.

[0025] The catalysts disclosed herein comprise gold (Au) combined with another metal (i.e., a second metal) on an oxide support, where the gold is present in an amount of at least 0.01 wt. % and the second metal is present in an amount of at least 0.005 wt. % based on the total weight of the catalyst. As will be understood by those skilled in the art, the activity and long-term performance of a catalyst are directly correlated to the metal loading. At the low metal loadings of the catalysts disclosed herein (e.g., catalyst 42), activity and long-term performance tend to be linearly correlated with metal loading over a wide range. Catalysts with very low loadings generally require very large reactor sizes to achieve maximum conversion. At very high metal loadings (e.g., greater than 5 wt. %), the linear correlation between activity and long-term performance at metal loading may be weaker due to precious metal overcapacity, diffusion limitations, and / or larger particle size. Optimizing the metal loading of a catalyst is highly dependent on the desired process configuration and conditions.

[0026] The metal loadings on the catalysts disclosed herein were determined using X-ray fluorescence (XRF). However, as will be appreciated by those skilled in the art, other techniques can also be used to measure the amount of metal on the catalyst. For example, the metal loading of the catalyst can also be measured using inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectroscopy (AAS). These measurement techniques can also be used to determine the level of contaminants on the catalyst. For the XRF method, wavelength dispersive X-ray fluorescence (WDXRF) spectroscopy was applied. Samples were milled using a Herzog HSM 100P disk mill at 1420 rpm for 1 minute, approximately 2000 kJ / min. 50 10 to 20 microns (μm) (d 90 The samples were prepared by grinding to a particle size of <80 μm. The samples were then mixed with a polyethylene wax binder (Ceridust 3620 from TER Chemicals) in a ratio of 80 wt% sample to 20 wt% binder and pressed into an alumina cup (40 mm diameter) using a Herzog HTP 40 press at 200 kN for 5 seconds to form a pill. The pill was then measured via WDXRF spectroscopy (Bruker AXS S8 Tiger 3kW) using the standard-free method Full Analysis Vac. Results were analyzed using Eval2 in SpectraPlus software (Bruker AXS V2.5.500), and a matrix correction was applied. For this matrix correction, the support material, in this case aluminum oxide (AlO), titanium oxide (TiO), or silicon oxide (SiO), was defined as the matrix of the sample to avoid overrepresentation of heavy elements relative to the light element support material.

[0027] Using this XRF method, both metal loading and contamination levels were calculated in wt% using the following definitions: Metal loading [wt%] = weight of precious metal [g] / total catalyst weight [g] Contamination level [wt%] = weight of contaminating element [g] / total catalyst weight [g] Based on this method, total metal loading can also be calculated using the following definitions: Total metal loading [wt%] = Metal loading [wt%] + Second metal loading [wt%] This means that if any additional Group VIIIB or Group IB metals are present, their corresponding metal loadings will be added to the total metal loading. The molar ratio between gold and the second metal is calculated using the following definition: Molar ratio Au / second metal=(metal loading amount Au / metal loading amount second metal) * (MW Second Metal / 197)

[0028] A particular aspect of the catalysts disclosed herein is the ratio between Au and the second metal. Surprisingly, it has been discovered that a higher Au content relative to the second metal results in greater catalyst stability when used to remove hydrogen at high oxygen partial pressures. The disclosed catalysts have an Au to second metal molar ratio of at least about 0.1. Below this level, the stabilizing effect of Au is limited, resulting in a catalyst with suboptimal performance. However, the more Au is loaded on the catalyst, the more the second metal benefits from the stabilizing effect of Au. The positive stabilizing effect of Au loading on the second metal may begin to plateau at molar ratios above 10. In commercial practice, catalyst performance can be optimized by limiting the Au to second metal molar ratio to about 1 to 5, thereby optimizing the benefit relative to the cost of the extra Au. Thus, by adding more second metal, more cost-effective and significant effects can be achieved.

[0029] Another aspect of the catalysts disclosed herein is a support based on a material having oxide properties. This includes well-known catalyst supports such as alumina, silica, silica-alumina, titania, zirconia, and mixtures thereof. Other less commonly used oxide supports, such as, but not limited to, magnesia, calcium oxide, chromia, ceria, lanthanum oxide, manganese oxide, zinc oxide, tin oxide, and combinations thereof, may also be used. The oxide support may include materials known to form an oxide outer surface when exposed to an oxygen atmosphere, such as metals, metal alloys, metal carbides, metal oxycarbides, metal nitrides, metal oxynitrides, and metal sulfides. As an example, it is well known in the art that silicon carbide, when exposed to oxygen, will form a silicon oxide layer several nanometers thick, resulting in surface properties similar, if not identical, to those of silica. The oxide support may also include materials that are mixtures between metal oxides and non-metal oxides. Examples of such supports include phosphates, borates, and sulfates. An example of such a material is aluminum phosphate.

[0030] The oxide support has a density of approximately 10 square meters per gram (m 2 / g). For example, the oxide support has a specific surface area of ​​about 20 m 2 / g, more preferably about 100m 2 / g, most preferably above 200m 2The support has a high specific surface area of ​​greater than 1 / g. The water pore volume or specific pore volume of the support is in the range of 0.30 cubic centimeters per gram (cc / g) to 1.00 cc / g. Preferably, the pore volume is in the range of 0.50 cc / g to 0.80 cc / g. The porosity of the support structure is in the range of about 40% by volume (vol.%) to 90 vol.%, preferably in the range of about 50 vol.% to 80 vol.%. Porosity is defined as the volume of pores in the support structure divided by the total volume of the support structure. The average pore size within the support structure depends on the support material, specific surface area, and porosity, and is generally in the range of about 2 nanometers (nm) to 50 nm. The support structure may be such that it has a bimodal pore size distribution. Thus, pores in the range of about 50 nm to 500 nm are also present. The surface area of ​​the catalyst support disclosed herein was determined by gas physisorption applying the BET method, ASTM D 3663. The porosity, specific pore volume, and pore size distribution of the support were determined by mercury intrusion porosimetry, ASTM test method D 4284. Measurement of the pore size distribution of the support can be measured by any suitable measuring device using a mercury surface tension of 474 dynes / cm at 25°C and a contact angle of 140 degrees.

[0031] The catalysts of the present disclosure may have a uniform distribution of Au metal and a second metal throughout the catalyst grains or repeating elements of the catalytically active structure catalyst (e.g., pellets). In certain embodiments, the catalyst may also have a specific metal distribution that is either eggshell, egg yolk, or egg white. In an eggshell-like distribution, the local metal concentration is highest at or near the outer surface of the catalyst structure, which may be a grain (e.g., a sphere, extrudate, or pellet), a structure (e.g., a monolith or foam), or a washcoat on such a structure. In an egg yolk distribution, the metal is present in the center of the catalyst structure, while in an egg white distribution, the metal concentration peaks somewhere between the center and the outer surface of the catalyst structure. Those skilled in the art will recognize preparation parameters that result in this metal distribution, such as by selecting the metal precursor, modifying the pH of the metal precursor solution, buffering the pH of the metal precursor solution, and / or adding an adsorption modifier to the metal precursor solution that will improve or attenuate the tendency of the metal precursor to adsorb to the support structure. Preferably, the Au metal and the second metal have a similar distribution throughout the support structure. However, in some cases, the distribution of each metal may be different, so that the local ratio between Au and the second metal may vary within the catalyst structure.

[0032] As discussed above and in more detail below, the disclosed catalysts are used for selective hydrogen removal at low inlet temperatures (e.g., preferably below 160°C, more preferably below 100°C) from O2-rich streams having O2 partial pressures of about 1 bar or greater, such as O2-rich streams produced from the electrolysis of water. Use of the disclosed catalysts for H2 removal from O2-rich streams may alleviate problems associated with using noble metal catalysts in oxidizing environments at low temperatures and high O2 partial pressures, and may result in O2 essentially free of H2. It should be understood that the disclosed catalysts are described in the context of a process for removing hydrogen from O2-rich streams produced in electrolyzers. However, the disclosed catalysts may be used in other processes for removing H2 from O2-rich streams (e.g., certain gas streams output by nuclear power plants) and in system configurations for producing H2-containing O2-rich streams. Furthermore, process conditions may vary without departing from the scope of the present disclosure. For example, the catalysts disclosed herein may be used when process conditions include low inlet temperatures (down to 60°C or even ambient temperature), high catalyst bed temperatures (up to 250°C or even 350°C), and high relative humidity of the water vapor (up to 90% or even 95%).

[0033] With the above in mind, Figure 2 is a flow diagram of a method 100 for making a bimetallic catalyst of the present disclosure. Method 100 includes preparing a metal salt impregnation solution (block 102). The metal salt impregnation solution may be prepared by any suitable technique. For example, a metal salt may be dissolved in a desired volume of a solvent (e.g., water). Metal salts used to prepare the impregnation solution include, but are not limited to, precious metal salts from metals belonging to Groups VIIIB and IB of the Periodic Table of the Elements, such as palladium salts and gold salts. As non-limiting examples, the palladium precursor used in the preparation of the impregnation solution for making palladium and gold-based catalysts is selected from the group of i) palladium salts consisting of palladium nitrate, palladium halides, chloropalladates, bromopalladates, palladium acetate, and palladium sulfate, or ii) chelated palladium complexes consisting of ammonia complexes of palladium, (poly)amine complexes of palladium (such as ethylenediamine and diethylenetriamine), (poly)carboxylic acid complexes of palladium (such as citric acid and gluconic acid), complexes of palladium combining carboxyl and amine groups (such as EDTA and NTA), amine acid complexes of palladium, and phosphine complexes of palladium, and the gold salt used in the preparation of the impregnation solution is selected from the group of gold salts consisting of gold nitrate, gold halides, chloroauric acid, chloroaurates, sodium bromoaurate, bromoaurates, dicyanoaurates, hydroxo gold(III) complexes, gold acetate, and gold sulfate. Preferred palladium salts are palladium halides, tetrachloropalladate, or palladium nitrate, and preferred gold salts are gold halides or chloroaurates. In certain embodiments, the impregnation solution is a colloidal solution of nanometer-sized particles containing a mixture of palladium and gold, either as salts or metals. In certain embodiments, when an organic solvent is used, the precursors may be organopalladium and organogold compounds. The solvent used to dissolve the precious metal precursors is water, alcohols, ketones, hydrocarbons, or other volatile solvents, and combinations thereof. In a preferred embodiment, the solvent is water.Other components may be added to the solvent to adjust the pH, promote absorption into the porous support, adjust the viscosity of the solvent, and / or control the interaction between the precursor and the support.

[0034] The amount of solvent used to dissolve the precious metal salt is preferably equal to the pore volume of the support. The relative amounts of palladium salt and gold salt in the impregnation solution are such that the catalyst of the present disclosure has about 0.005 wt% and 0.5 wt% palladium and about 0.01 wt% to 2 wt% gold. Catalysts with other metals can be made using similar precursors and through similar approaches.

[0035] After preparing the impregnation solution according to the act of block 102, the method 100 includes impregnating the support / carrier with the impregnation solution to form an impregnated support (block 106). For example, the impregnation solution may be sprayed onto the support at ambient temperature such that the pores of the support are filled with the impregnation solution. However, any other suitable impregnation technique, such as incipient wetness impregnation, immersion impregnation, and wet impregnation, may be used to completely impregnate the pore structure of the support. In one embodiment, only a portion of the support pore volume is impregnated with the impregnation solution. In this particular embodiment, the solution is sprayed in a fine spray while the support is tumbled in a rotating drum to achieve a uniform distribution on the support.

[0036] After the support is impregnated according to block 106, the precious metal in the impregnated support is reduced to form a reduced-metal-impregnated support (block 108). For example, reduction is accomplished by treating the impregnated support with a solution having a reducing agent. The reducing agent may be any suitable reducing agent, such as, for example, hydrazine (NH), formic acid, formate, formaldehyde, acetaldehyde, and sodium borohydride. The addition volume of the reducing agent solution is at least 80% compared to the pore volume. If the addition volume is significantly greater than the pore volume, the excess reducing agent solution is decanted after the reduction is complete.

[0037] In certain embodiments, the reducing agent may already be added to the impregnation solution, whereby the reduction is completed by increasing the temperature after impregnation of the combined solution.

[0038] The method 100 also includes drying the reduced metal-impregnated support to form a first dried impregnated support (block 120). For example, the impregnated support is dried for 5 to 30 minutes in a flow of air having an air temperature of about 80° C. to about 175° C. After the drying step performed in block 120, the residual solvent on the support is less than about 5 wt % compared to the weight of the support.

[0039] In certain embodiments, the reduced metal-impregnated support may be equilibrated prior to decanting and drying to ensure that the porous support / carrier absorbs any remaining amounts of the impregnation solution and / or added reducing agent solution, allowing the reduction of the impregnated metal to proceed to its maximum degree of reduction. That is, the support / carrier and impregnation solution are tumbled together for a sufficient time to allow equilibration to occur such that the support can no longer take up (absorb) the impregnation solution and / or reducing agent solution, and to allow sufficient time to reach adequate reduction of the metal precursor to produce the reduced metal. The temperature of the reduced metal-impregnated support may be increased to achieve a faster degree of reduction.

[0040] In an optional step, after drying according to block 120, the first dried impregnated support may undergo a washing step to form a washed impregnated support (block 124). For example, the first dried impregnated support may be washed with a volume of washing fluid (e.g., deionized water or a solution containing non-halogen ions) to remove contaminants such as, but not limited to, sodium, potassium, chloride, bromide, or any other elements that may undesirably affect the performance of the catalyst. To facilitate cleaning of the internal pores of the porous support, the volume of water in the first washing step should be greater than the pore volume of the first dried impregnated support. The volume of washing fluid added during subsequent washing steps may be approximately equal to the volume of the support. After the first or subsequent addition of washing fluid, the impregnated support is left with the washing fluid for several minutes to allow diffusion of contaminants from the porous support. After each washing step, excess washing fluid may be removed by decantation. This washing is repeated until the washed impregnated support is essentially free of contaminants. The level of contaminants on the catalyst was assessed using X-ray fluorescence (XRF), however, inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectroscopy (AAS) can also be used to determine the level of contaminants on the catalyst.

[0041] The method 100 also includes drying the washed impregnated support to form a second dried impregnated support (block 126) and, optionally, heating the second dried impregnated support to form a catalyst (block 130). For example, the washed impregnated support is dried in air at a temperature of about 100°C to about 175°C for 4 to 8 hours. After drying the washed impregnated support, the residual solvent on the second dried impregnated support is less than about 5 wt% compared to the weight of the support. After the drying step of block 126, the second dried impregnated support may optionally be subjected to a heat treatment or series of heat treatments. During such heat treatments, the catalyst is heated at a temperature ranging from about 250°C to 600°C for 10 minutes to 2 hours. The heat treatments may be performed in air or an inert gas, or both. This heat treatment serves to remove non-ash-producing species, such as residual nitrates, carbonates, or other carbon- or nitrogen-containing molecules, from the catalyst.

[0042] In embodiments in which the dried, impregnated support is heat-treated according to the act of block 130, preferably, at least one heat treatment is performed in a reducing atmosphere, preferably a hydrogen-containing atmosphere. Preferably, the at least one heat treatment (e.g., a reducing heat treatment) is performed after an oxidizing or inert heat treatment, or, in certain embodiments, as a replacement for an oxidizing or inert heat treatment. If other components in the hydrogen-containing gas used in the at least one heat treatment have inert properties (such as argon, nitrogen, and helium present in the hydrogen-containing gas), the hydrogen concentration may be lower (e.g., below 95% compared to a hydrogen-containing gas without the component having inert properties) and still achieve the desired reduction effect. To enable adequate reaction rates, preferably, the hydrogen concentration in the hydrogen-containing gas is greater than 1% by volume. During this at least one heat treatment, the catalyst is heated at a temperature ranging from about 250°C to 400°C for 10 minutes to 2 hours.

[0043] The reduction heat treatment can be carried out in a separate unit as the oxidation treatment, but it is preferred to use separate units for the oxidation and reduction heat treatments. In a preferred embodiment, the reduction heat treatment is carried out in the same reactor unit in which the actual catalyst removal reaction will occur. Such reduction heat treatments can also be carried out to regenerate or rejuvenate spent catalyst. This can be carried out outside the reactor unit in which the actual catalyst removal reaction will occur, or inside the reactor unit.

[0044] As will be appreciated, the method by which a catalyst is prepared affects its properties, such as the particle size of the metal particles in the support. Such particle size can affect catalyst performance. The metal particle size present within the internal pore volume of the oxide support of the disclosed catalysts can be in the nanometer range. This is highly desirable because gold and the second metal are very expensive. Therefore, maximizing catalytic performance per unit of precious metal mass is important. This is achieved by nanometer-sized metal alloy particles (i.e., gold-second metal alloy particles). However, when the particle size of the majority of metal alloy particles becomes very small (e.g., below 4 nm), the surface chemistry of these metal alloys can change dramatically, potentially resulting in completely different catalytic behavior. As a result, catalytic performance per unit of precious metal mass can decrease dramatically with very small particles. As will be appreciated by those skilled in the art, this requires optimization to maximize catalytic activity.

[0045] The particle size of metal nanoparticles can be measured using any suitable technique known in the art. As a non-limiting example, the particle size of metal nanoparticles can be measured using transmission electron microscopy, X-ray photoelectron microscopy (XPS), and chemisorption, among others. As will be appreciated by those skilled in the art, the particle size of metal particles can vary depending on the measurement technique. For example, when using CO chemisorption, the metal particle size of the catalyst disclosed herein exhibited an average particle size of 16 nm. However, when using transmission electron microscopy, for example, the particle size of the metal particles of the catalyst disclosed herein revealed that most metal particles had diameters less than 50 nm, with most particles having diameters between 2 nm and 27 nm, and the average particle size was 6.5 nm.

[0046] As will be understood by those skilled in the art, the surface composition of metal particles on a catalyst determines its catalytic properties. Such surface composition can be significantly different from the bulk composition of the metal particles, and as a result, activity is not necessarily governed by the bulk composition of the metal particles. The metal distribution within each metal particle, particularly its surface composition, can be strongly dependent on the conditions during catalyst preparation and / or catalyst pretreatment. Furthermore, the metal distribution and / or surface composition of a catalyst can change during use in a system process. Catalytic activity can be improved or weakened by changing system operating conditions such that the surface composition changes.

[0047] Catalyst Compositions Tested for Catalytic Activity Example 1 - The present invention This Example 1 describes the preparation of Catalyst 1, which represents a catalyst of the present invention.

[0048] The impregnation solution is prepared by dissolving an amount of sodium tetrachloropalladate (NaPdCl) and chloroauric acid (HAuCl) in a volume of water equal to the water pore volume of the alumina support, such that the solution concentration is approximately 0.1 wt% Pd and 0.05 wt% Au on the final catalyst. The impregnation solution is sprayed onto the alumina support at ambient temperature. The alumina support is then heated to approximately 210 m 2 The impregnated alumina support is a spherical alumina support having a diameter of 2.5 mm, a BET surface area of ​​0.78 milliliters per gram (ml / g), and a pore volume of approximately 0.78 milliliters per gram (ml / g). The impregnated alumina support is treated with a volume of 2.3 wt% hydrazine (NH) solution to reduce the Pd and Au in the impregnated alumina support. The volume of the hydrazine solution is approximately equal to the pore volume of the alumina support. After reduction, the resulting support and the hydrazine solution are tumbled together for 10 minutes to allow equilibration, ensuring that the support has absorbed the maximum amount of hydrazine. After completing the reduction reaction, the resulting support is dried in air at 150°C for 45 minutes, thereby forming a first dried impregnated support. The first dried impregnated support is washed stepwise with volumes of distilled or deionized water until the resulting wash water is essentially chloride-free. The volume of distilled or deionized water is approximately equal to the volume of the first dried impregnated support. After decanting the excess wash water, the washed impregnated support is dried at 120°C for about 6 hours to form a second dried impregnated support. The second dried impregnated support used contained 0.102 wt% Pd, 0.050 wt% Au, and 0.009 wt% chloride as determined by XRF. The second dried impregnated support is heated in a hydrogen atmosphere at 300°C for about 1 hour to form the catalyst of the present invention.

[0049] Example 2 - Comparative Example This Example 2 describes the preparation of Catalyst 2, which represents a comparative catalyst.

[0050] The impregnation solution is made by dissolving an amount of palladium nitrate (Pd(NO3)2) in a volume of water equal to the water pore volume of the alumina support, resulting in approximately 0.1 wt% Pd on the final catalyst. The impregnation solution is sprayed onto the alumina support at ambient temperature. The alumina support is then heated to approximately 210 ml. 2 The alumina support is a spherical alumina support having a diameter of 2.5 mm, a BET surface area of ​​0.78 milliliters per gram (ml / g), and a pore volume of approximately 0.78 milliliters per gram (ml / g), corresponding to a porosity of 75%. After impregnation, the impregnated alumina support is conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours, thereby forming a dried catalyst. The dried catalyst is calcined at 450°C for 3 hours and then treated with a volume of 2.3 wt% hydrazine (NH) solution to reduce the Pd in ​​the impregnated alumina support. The volume of the hydrazine solution is approximately equal to the pore volume of the alumina support. After reduction, the resulting support is pre-dried at 150°C for 45 minutes, and then dried at 120°C for 6 hours, thereby forming a dried impregnated support. The dried impregnated support is heated in a hydrogen atmosphere at 300°C for approximately 1 hour to form the catalyst of the present invention.

[0051] Example 3 - Comparative Example This Example 3 describes the preparation of Catalyst 3, which represents a comparative catalyst.

[0052] The impregnation solution is made by dissolving an amount of palladium nitrate (Pd(NO3)2) in a volume of water equal to the water pore volume of the alumina support, resulting in approximately 0.5 wt% Pd on the final catalyst. The impregnation solution is sprayed onto the alumina support at ambient temperature. The alumina support is then heated to approximately 210 ml. 2The alumina support is a spherical alumina support having a diameter of 2.5 mm, a BET surface area of ​​0.78 milliliters per gram (ml / g), and a pore volume of approximately 0.78 milliliters per gram (ml / g), corresponding to a porosity of 75%. After impregnation, the impregnated alumina support is conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours, thereby forming a dried catalyst. The dried catalyst is calcined at 450°C for 3 hours and then treated with a 2.3 wt% hydrazine (NH) solution to reduce the Pd in ​​the impregnated alumina support. The volume of the hydrazine solution is approximately equal to the pore volume of the alumina support. After reduction, the resulting support is pre-dried at 150°C for 45 minutes, followed by drying at 120°C for 6 hours, thereby forming a dried impregnated support. The dried impregnated support is heated in a hydrogen atmosphere at 300°C for approximately 1 hour to form the catalyst of the present invention.

[0053] Example 4 - Comparative Example This Example 4 describes the preparation of Catalyst 4, which represents a comparative catalyst.

[0054] The impregnation solution is made by dissolving an amount of palladium nitrate (Pd(NO3)2) and platinum nitrate (Pt(NO3)2) in a volume of water equal to the water pore volume of the alumina support, resulting in about 0.1 wt% Pd and about 0.05 wt% Pt on the final catalyst. The impregnation solution is sprayed onto the alumina support at ambient temperature. The alumina support is then heated to about 210 m 2The alumina support is a spherical alumina support having a diameter of 2.5 mm, a BET surface area of ​​0.78 milliliters per gram (ml / g), and a pore volume of approximately 0.78 milliliters per gram (ml / g), corresponding to a porosity of 75%. After impregnation, the impregnated alumina support is conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours, thereby forming a dried catalyst. The dried catalyst is calcined at 450°C for 3 hours and then treated with a volume of 2.3 wt% hydrazine (NH) solution to reduce the Pd and Pt in the impregnated alumina support. The volume of the hydrazine solution is approximately equal to the pore volume of the alumina support. After reduction, the resulting support is pre-dried at 150°C for 45 minutes, and then dried at 120°C for 6 hours, thereby forming a dried impregnated support. The dried impregnated support is heated in a hydrogen atmosphere at 300°C for approximately 1 hour to form the catalyst of the present invention.

[0055] Example 5 - Comparative Example This Example 5 describes the preparation of Catalyst 5, which represents a comparative catalyst.

[0056] The impregnation solution is made by dissolving an amount of palladium nitrate (Pd(NO3)2) and silver nitrate (AgNO3) in a volume of water equal to the water pore volume of the alumina support, resulting in about 0.1 wt% Pd and about 0.05 wt% Ag on the final catalyst. The impregnation solution is sprayed onto the alumina support at ambient temperature. The alumina support is then heated to about 210 m 2The alumina support is a spherical alumina support having a diameter of 2.5 mm, a BET surface area of ​​0.78 milliliters per gram (ml / g), and a pore volume of approximately 0.78 milliliters per gram (ml / g), corresponding to a porosity of 75%. After impregnation, the impregnated alumina support is conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours, thereby forming a dried catalyst. The dried catalyst is calcined at 450°C for 3 hours and then treated with a volume of 2.3 wt% hydrazine (NH) solution to reduce the Pd and Ag in the impregnated alumina support. The volume of the hydrazine solution is approximately equal to the pore volume of the alumina support. After reduction, the resulting support is pre-dried at 150°C for 45 minutes, and then dried at 120°C for 6 hours, thereby forming a dried impregnated support. The dried impregnated support is heated in a hydrogen atmosphere at 300°C for approximately 1 hour to form the catalyst of the present invention.

[0057] Example 6 - Comparative This Example 6 describes the preparation of Catalyst 7, which represents a comparative catalyst containing only Pt.

[0058] The impregnation solution is made by dissolving a quantity of platinum nitrate (Pt(NO3)2) in a volume of water equal to the water pore volume of the alumina support, resulting in approximately 0.3 wt% Pt on the final catalyst. The impregnation solution is sprayed onto the alumina support at ambient temperature. The alumina support is then heated to approximately 210 m 2 The alumina support is a spherical alumina support having a diameter of 2.5 mm, a BET surface area of ​​0.78 milliliters per gram (ml / g), and a pore volume of approximately 0.78 milliliters per gram (ml / g), corresponding to a porosity of 75%. After impregnation, the impregnated alumina support is conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours, thereby forming a dried catalyst. The dried catalyst is calcined at 450°C for 3 hours and then treated with a volume of 2.3 wt% hydrazine (NH) solution to reduce the Pt in the impregnated alumina support. The volume of the hydrazine solution is approximately equal to the pore volume of the alumina support. After reduction, the resulting support is pre-dried at 150°C for 45 minutes, followed by drying at 120°C for 6 hours, thereby forming a dried impregnated support. The dried impregnated support is heated in a hydrogen atmosphere at 300°C for approximately 1 hour to form the catalyst of the present invention.

[0059] Example 7 - Comparative Example This Example 7 describes the preparation of Catalyst 7, which represents a comparative catalyst containing only Au.

[0060] The impregnation solution is made by dissolving an amount of chloroauric acid (HAuCl4) in a volume of water equal to the water pore volume of the alumina support, such that the concentration of the solution is about 0.1 wt% Au on the final catalyst. The impregnation solution is sprayed onto the alumina support at ambient temperature. The alumina support is then heated to about 210 ml. 2 The impregnated alumina support is a spherical alumina support having a diameter of 2.5 mm, a BET surface area of ​​0.78 milliliters per gram (ml / g), and a pore volume of approximately 0.78 milliliters per gram (ml / g). The impregnated alumina support is treated with a volume of 54 wt% sodium formate solution to reduce the Au in the impregnated alumina support. The volume of the sodium formate solution is approximately equal to the pore volume of the alumina support. After reduction, the resulting support and the sodium formate solution are tumbled together for 10 minutes to allow equilibration, ensuring that the support has absorbed the maximum amount of sodium formate. After completing the reduction reaction, the resulting support is dried in air at 150°C for 45 minutes, thereby forming a first dried impregnated support. The first dried impregnated support is washed stepwise with volumes of distilled or deionized water until the resulting wash water is essentially chloride-free. The volume of distilled or deionized water is approximately equal to the volume of the first dried impregnated support. After decanting the excess wash water, the washed impregnated support is dried at 120°C for about 6 hours to form a second dried impregnated support. The second dried impregnated support is heated in a hydrogen atmosphere at 300°C for about 1 hour to form the catalyst of the present invention.

[0061] Table 2 below provides the properties of Selective Hydrogenation Catalysts 1-7 of Examples 1-7 above.

[0062] [Table 2]

[0063] Example 8 - Performance Test Example 8 describes performance tests conducted to characterize the hydrogen removal activity of the catalyst compositions of Examples 1-7.

[0064] Experimental conditions were chosen that closely resembled those used for hydrogen removal from O2-rich streams, with a feed gas composition representative of electrolyzer O2 off-gas. For example, a laboratory reactor was loaded with 15 mL of catalyst. An O2-rich feed with 1000 ppm H2 and 3.5 vol% water vapor (corresponding to a partial pressure of 0.17 bar and a dew point of 57°C) was fed to the reactor at a rate that provided a GHSV of 2500 v / vh. The reactor was operated at three different temperatures: 80°C, 120°C, and 160°C, with an O2 partial pressure of 5 bar.

[0065] Table 3 illustrates the performance of Catalysts 1-7 in Examples 1-7 as a function of temperature. As can be seen from Table 3, when using the catalyst of the present invention (Example 1), the H concentration in the O-rich gas stream at temperatures ranging from 80°C to 160°C is reduced from 1000 ppmv to less than about 10 ppmv. In contrast, O-rich gas streams treated with catalysts not containing Au (e.g., Examples 3-6) and catalysts having only Au (e.g., Example 7) had H concentrations of 400 ppmv or more at 80°C. Even at 120°C, O-rich gas streams treated with certain comparative catalysts (e.g., Examples 2, 4, 5, and 7) had H concentrations exceeding 150 ppmv. Only after increasing the reaction temperature to 160°C did catalysts having either Pd / Pt or high Pd loadings reduce the H concentration in the O-rich gas stream to levels comparable to those of the Pd / Au catalyst of the present invention. Thus, inventive catalyst 1 removed H from an O2-rich gas stream at temperatures below 120°C, with the resulting O2-rich gas stream having an H2 concentration of less than about 10 ppmv. From these examples, it is clear that when Au is added to Pd, it results in significantly improved performance. On the other hand, the very low conversion across the entire temperature range for example 7 illustrates that it is not the Au itself that causes the activity. Without being bound by theory, it is believed that the addition of Au to the catalyst results in a more oxidation-resistant catalyst system.

[0066] Table 3 below shows the outlet hydrogen concentration (ppmv) for each catalyst sample at three different temperatures.

[0067] [Table 3]

[0068] Catalyst Compositions Tested for Catalytic Stability Examples 9-20 - The present invention These examples describe the preparation of catalysts 9-20, which represent catalysts of the present invention.

[0069] Catalysts 9–20 were prepared in the same manner, varying the metal precursor salts, their respective concentrations, and the support, as summarized in Table 4.

[0070] The impregnation solution is prepared by dissolving a certain amount of chloroauric acid (HAuCl4) as the Au precursor and a second metal precursor in a volume of water equal to the pore volume of the oxide support, such that the concentration of the solution after evaporation will result in the desired concentration of metal on the final catalyst. The precursor solution is sprayed onto the oxide support at ambient temperature. The impregnated oxide support is dried in air at 65°C for 15 minutes, thereby forming a first dried impregnated support. The dried impregnated support is treated with 20 g / ml of ascorbic acid solution to reduce the metal in the impregnated support. The volume of ascorbic acid solution added is approximately equal to the pore volume of the oxide support. Following this reduction step, the resulting support and ascorbic acid solution are tumbled together for 10 minutes to equilibrate, ensuring that the support has absorbed the maximum amount of ascorbic acid and completing the reduction reaction. The resulting reduced support is washed six times with a certain volume of deionized water. Deionized water is added in a volume three times the volume of the first dried, impregnated support, and the support and washings are then tumbled together for 10 minutes between washes. After each wash, the liquid is decanted. Following the washing steps, the washed, impregnated support is dried at 120°C for approximately 6 hours to form a second, dried, impregnated support.

[0071] As discussed above, the metal precursors and oxide supports for catalysts 9-20 are summarized in Table 4 below. The alumina support was approximately 210 m 2 The alumina support is a 1.8 mm diameter spherical support having a BET surface area of ​​0.65 milliliters per gram (ml / g) and a pore volume of about 0.65 milliliters per gram (ml / g). The titania support contains anatase as the titania phase and has a pore volume of about 45 ml / g. 2 The silica support is a trilobe extrudate of 1.6 mm diameter with a BET surface area of ​​about 0.32 mL / g and a pore volume of about 0.32 mL / g. 2 / g and a pore volume of about 0.85 mL / g.

[0072] Examples 21 to 23 - Comparative Examples These examples describe the preparation of catalysts 21-23, which represent comparative catalysts.

[0073] Catalysts 21 to 23 were prepared in the same manner as catalysts 9 to 20. Catalysts 21 to 23 contain a single metal, and their compositions, respective metal precursors, and oxide supports are summarized in Table 3.

[0074] Example 24 - Performance Testing Example 24 describes performance tests conducted to characterize the stability of the catalyst compositions of Catalysts 9-23.

[0075] The experimental conditions selected were very similar to those used for hydrogen removal from an O2-rich stream, with a feed gas composition typical of electrolyzer O2 off-gas. To determine the catalyst's stability, each tested catalyst sample was subjected to a temperature of 230 °C, which is typical in an adiabatic reactor where the temperature rises significantly due to reactor heat generation. A laboratory reactor was filled with 1 mL of each catalyst sample. The catalyst samples were exposed to a pure oxygen stream at 4 bar absolute pressure at 230 °C for 48 hours. Before and after this treatment, the activity of the catalyst samples was evaluated using an oxygen-rich feed with 5000 ppm H2 and a flow rate providing a GHSV of 25,000 v / vh. The reactor was operated at an O2 partial pressure of 1.4 bar and a temperature of 50 °C. Based on the hydrogen conversion rate in the reactor, a first-order activity constant was determined according to the following equation: k A [s -1 ]=H2 flow rate [mol / s / m 3 ] * LN(1 / (1-H2 conversion rate)) / H2 concentration [mol / m 3 ] In the formula, k A [s -1 ] is the first order activity constant of the catalyst and the term LN is the natural logarithm, whereby the H2 conversion is defined as: H2 conversion rate = (H2 inlet concentration [mol / m 3 ]-H2 outlet concentration [mol / m 3 ]) / H2 inlet concentration [mol / m 3 ]).

[0076] A comparison of the activity constants before and after high temperature treatment provides an index of stability. The stability ratio is defined as: stability ratio=k A (After high temperature treatment) / k A (Before high temperature treatment)

[0077] A stability ratio below 1 indicates deactivation, while a stability ratio near or even above 1 indicates high stability or even autoactivation.

[0078] Table 4 below shows the composition of various catalysts, Catalysts 9-23, as well as their first-order activity constants, k, after prolonged exposure to oxygen at 230°C and 4 bara. A , and stability ratio.

[0079] [Table 4] * TiO2 supported, ** SiO2 support

[0080] As shown in Table 4, the activity and stability ratios of catalysts 9-15 of the present invention are better than those of catalyst 21, indicating that Pd-containing catalysts (e.g., catalysts 9-15) benefit from the addition of Au. Pd-containing catalysts without Au (e.g., catalysts 21 and 22) have lower stability ratios and lower activity after high-temperature treatment compared to Pd-Au catalysts 9-15 of the present invention. Comparing the activity and stability ratios of Pt-Au catalysts 16 and 17 of the present invention with that of catalyst 22 reveals that Pt-containing catalysts also benefit from the addition of Au. Pt-containing catalysts without Au (e.g., catalyst 22) have lower stability ratios and lower activity after high-temperature treatment compared to Pt-Au catalysts 16 and 17 of the present invention. Similar to monometallic catalysts having only Pd or Pt as the active metal, catalysts having Au as the single active metal also have lower stability and lower activity after high-temperature treatment. For example, as shown in Table 4, the activity and stability ratios of inventive catalysts 10 and 17 are higher compared to the activity and stability ratios of catalyst 23, which contains the same Au loading as inventive catalysts 10 and 17. It is clear that Pd, Pt, and Au alone are not sufficient to achieve the activity and stability ratios observed in inventive catalysts 9-20 for the application of removing H from an O-rich stream. Rather, the improved activity and stability ratios are the result of the combination of Au with another noble metal (i.e., a second metal).

[0081] Furthermore, as shown in Table 4, the catalytic stability of inventive catalysts 9-15 improves with increasing Au content and Au / second metal molar ratio. Similarly, comparing inventive catalysts 16 and 17, improved stability is observed with increasing Au content and Au / second metal molar ratio.

[0082] Furthermore, comparing the stability of inventive catalysts 13 and 20, it is clear that at low Au and secondary metal loadings, the stability ratio exceeds 1, indicating the high stability of these catalysts. Furthermore, catalyst 20 has higher stability at a lower metal loading of 0.03 wt% compared to comparative catalysts 21 and 22, which have total metal loadings of 0.1 wt% Pd and 0.1 wt% Pt, respectively. It should be noted that the choice of Pd precursor used in preparing the catalyst is not critical. For example, inventive catalysts 10 and 12 have comparable activity and stability, as shown in Table 4.

[0083] The effect of different oxide supports on catalyst activity and stability was also evaluated. As shown in Table 4, catalysts 9 and 11 of the present invention, which use alumina as the oxide support, have similar activity compared to catalysts 18 and 19 of the present invention, which use titania and silica as the oxide support, respectively. At the same metal loading for each of catalysts 9, 11, 18, and 19, all of these catalysts exhibited activity between 45 and 300 m 2 Despite the fact that we have different oxide supports and geometries with surface areas ranging from 8 to 15 s after deactivation tests at 230 °C, -1 Without being bound by theory, the stabilization effect appears to be governed by the presence of Au in the catalyst and, to a lesser extent, by the nature and properties of the oxide support.

[0084] The technical effect of using the catalysts disclosed herein for H removal from O2-rich gas streams, such as those produced in electrolyzers, is to provide effective and efficient H2 removal at temperatures below 160°C, particularly below 100°C, under oxidizing conditions with high oxygen partial pressures. The addition of Au to these catalysts mitigates catalyst oxidation and improves the H2 removal performance of the catalyst at O2 partial pressures above 1 bar, particularly 5 bar or greater. Thus, it is the addition of Au in combination with a second metal that provides desirable H2 removal activity at low temperatures (e.g., below 160°C) under oxidizing conditions (e.g., O2 partial pressures above 1 bar).

[0085] The present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the present disclosure is, therefore, indicated by the appended claims rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. 1. A process for removing hydrogen from an oxygen gas stream, comprising: electrolyzing water in an electrolytic cell to produce a hydrogen-rich stream and an oxygen-rich stream, the oxygen-rich stream comprising hydrogen; feeding the oxygen-rich stream to a reactor containing a gold-containing catalyst; contacting the oxygen-rich stream with the gold-containing catalyst in the reactor, wherein the gold-containing catalyst comprises gold and a second metal on an oxide support, and wherein the oxygen-rich stream in the reactor has an oxygen partial pressure greater than 1 bar.

2. 10. The process of claim 1, wherein the temperature at the reactor inlet is from 40 degrees Celsius (°C) to 160°C.

3. 3. The process of claim 1 or 2, wherein greater than 95% of the hydrogen is removed from the oxygen gas stream.

4. The process of any one of claims 1 to 3, wherein the second metal is selected from Group VIIIB and / or Group IB metals of the Periodic Table of the Elements.

5. 5. The process of claim 4, wherein the second metal is palladium, platinum, or rhodium.

6. 6. The process of claim 5, wherein the second metal is present in an amount of at least 0.005 wt % and the gold is present in an amount of at least 0.01 wt %.

7. 7. The process of claim 6, wherein the amount of the second metal is measured by X-ray fluorescence (XRF).

8. The process of any one of claims 1 to 7, wherein the molar ratio of the gold to the second metal is at least 0.

1.

9. 9. The process according to any one of claims 1 to 8, wherein the gold-containing catalyst has a porosity of 40% by volume (vol.%) to 90% by volume, preferably 50% to 80% by volume.

10. 10. The process of claim 9, wherein the porosity is measured by mercury intrusion porosity according to ASTM test method D 4284.

11. The oxide support has a surface area of ​​10 square meters per gram (m ２ 11. The process according to claim 1, wherein the sintered body has a specific surface area of ​​more than 1000 W / g.

12. The specific surface area is 20 m ２ / g, preferably more than 100m ２ / g, most preferably 200m ２ The process of any one of claims 1 to 11, wherein the hydroxyl group is 0.15 to 0.25g.

13. 13. The process according to claim 11 or 12, wherein the specific surface area is measured by gas physisorption according to the BET method, ASTM D 3663.

14. 14. The process of any one of claims 1 to 13, wherein the gold is present in an amount of at least 0.01 weight percent (wt.%).

15. 15. The process of claim 14, wherein the amount of gold is measured by XRF.

16. The process of any one of claims 1 to 15, wherein the oxide support is alumina, silica, silica-alumina, titania, zirconia, and combinations thereof.

17. 17. The process of any one of claims 1 to 16, wherein the total metal content of the gold-containing catalyst is from 0.03 wt% to 2.1 wt%.

18. 18. The process of claim 17, wherein the total metal content is measured by XRF.

19. 19. The process of any one of claims 1 to 18, wherein at least the gold or the second metal in the catalyst has an average particle size of greater than 4 nanometers (nm).

20. 20. The process of claim 19, wherein the average particle size is measured by CO chemisorption.

21. 20. The process of claim 19, wherein the average particle size is measured by TEM.

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